1. Field of Invention
This invention relates to processes for the dewatering of phosphate slimes. More specifically, this invention relates to an electro-sedimentation process for the dewatering of phosphate slimes.
2. Prior Art
The main commercial source for the production of phosphates and phosphorus is phosphate rock which is largely apatite. During the mining and processing of phosphate rock a residual material known as phosphate slime is commonly produced. It is an aqueous suspension or gel of insoluble phosphate rock, phosphate clay and/or apatite in water. Because of its collodial nature which makes filtration impossible, it cannot be treated by ordinary procedures to recover the phosphates contained therein. It is necessary to store such slimes in settling ponds because no other means of disposition of this material is commercially feasible.
The problem of dewatering phosphate slimes, slurries and muds is especially troublesome because the slimes generally fail to settle out principally because of the small size of the particulate material. Because of the hydrophilic nature of the phosphate slime, the solid content of the slime, even if placed in a settling pond for considerable periods of time, rarely rises above 10 to 15%. Further, these settling ponds are unattractive and hazardous and take land out of productive use. In addition, they retain water which is often used in the mining operation and require maintenance of the walls of the ponds to prevent breaches in the ponds which would allow the escape of the slime. Use of these large settling ponds has been a subject of great concern, particularly in the State of Florida, where hundreds of thousands of acres of otherwise productive land have been more or less permanently converted to slime disposal areas with thousands of additional acres of land being converted each year. This represents a tremendous loss in land, water and minerals for the state.
When created the slime in the settling ponds has a solid content of only about 3 to 5% and takes about six months to settle to a solid content of as much as 15%. In view of the above, it is clear that there is a significant need for improved processes for the dewatering of slimes to convert them into potentially useful products and to return the land to a more productive use.
Numerous efforts and proposals have been offered to improve the rate of dewatering phosphate slimes, including at least the following:
(a) The U.S. Bureau of Mines has been active in this field, see reports R17892, 8089, 8498 and 6451. PA1 (b) Dr. Henry L. Barwood et al of the Florida Phosphate Research Institute has published a draft entitled "Phosphate Clay Waste Bibliography." PA1 (c) Leslie G. Bromwell et al of the Florida Phosphate Clays Research Project has extensively researched the subject, see pages 541-558 of an article entitled "Waste Clay Dewatering and Disposal." PA1 (d) An overview of the subject appears in the November 1977 issue of World Mining, pages 62-64. PA1 (e) Stanczyk, MH, Feld, I. L., Electro-dewatering Tests of Florida Phosphate Rock Slime, U.S. Dept. of the Interior, Bureau of Mines (1964). PA1 (f) McKean, J. E.; ECOPAC Field Test in Florida Phosphate Slime Pond, Monsanto Enviro-Chem (Jan. 21, 1986). PA1 (g) El-Shell, H. E.; Beneficiation Research - Clay Disposal. PA1 (1) Placing an anode at the bottom of a holding facility for the holding of the phosphate slime; PA1 (2) Filling the holding facility with phosphate slime; PA1 (3) Placing a cathode on the surface of the phosphate slime but below the surface of any supernatant water such that said cathode retains contact with the phosphate slime; and PA1 (4) Applying a sufficient electrical current to the cathode to produce a partial separation of clay particles contained within the phosphate slime from liquid to produce an improved phosphate slime with a solid content of at least about 15%.
A number of patents have also disclosed attempts to resolve this problem, including U.S. Patent Nos. 3,450,633; 3,680,698; 3,761,239; 3,763,041; 4,000,067; 4,107,026; 4,155,233; 4,194,960; 4,217,212; 4,229,293; 4,330,685; 4,563,285; 4,608,179 and 4,808,304. See also British Patent No. 1,466,185. See also Development of Alternatives for Dewatering Dredged Material, Halibarton, pages 615-631.
In particular, U.S. Patent No. 4,808,304 discloses an apparatus for the dewatering of phosphate slime using a closed loop system incorporating an electrokinetic densification of the dredged material. While U.S. Pat. No. 4,808,304 utilizes an electrokinetic process for the dewatering of phosphate slime, the cost of the electricity used in this process is prohibitive and the solid content of the material produced is still not greater than about 14 to 18%.
Therefore, it is an object of this invention to provide an improved process for the dewatering of phosphate slimes.
It is another object of this invention to provide an improved process for the dewatering of phosphates using an improved electro-sedimentation process.
It is a still further object of this invention to provide an improved process for the dewatering of phosphate slimes where electrical energy is used, utilizing different electrical wave forms.
These and other objects and features of this present invention will become apparent to those skilled in the art from a consideration of the following detailed description, drawings and claims. The description along with accompanying drawings provides a selected example of construction of the device to illustrate the invention.